1. Field of the Invention
This invention relates to a side seal used in a linear motion guide unit which moves along rails.
2. Description of the Related Art
As shown in FIG. 5, a side seal used in such a well-known type of liner motion guide unit is formed of a combination of a metal-made plate and a rubber-made elastic material baked onto the surface thereof. The side seal includes a seal lip Ha making contact with the track surface of the rail, and is provided for preventing the intrusion of foreign substances and the like into a slider while the slider moves on the rail with the rotation of a drive shaft 5 formed of a screw. End caps C are attached to each of the opposite ends of the slider S in the moving direction of the slider S moving along the rails 1. A seal body 2 of the side seal is attached to the outer face of each of the end caps C, i.e., the face opposite to the contact face of the end cap C with the slider S.
The slider S is equipped with guide passages (not shown) and a plurality of rolling elements such as balls, rollers or the like (not shown) is mounted in the guide passages in such a manner as to be able to roll therein. Each of the guide passages extends endlessly by the interposition of rolling-element directing passages which are respectively provided in the end caps C on the opposite ends of the slider S, and thereby the rolling elements roll along a raceway 1a formed on the rail 1 while being guided by the guide passage. In the process of the rolling elements rolling on the raceway 1a of the rail 1 in this manner, the bearing function is implemented to achieve smooth movement of the slider S.
The end cap C has a lubricant supply port formed therein, and the seal body 2 has a supply port formed therein to be fluidly connected to the lubricant supply port. As shown in FIG. 4, such a supply port is covered with a grease nipple 3. The grease nipple 3 protrudes outward in the axis direction which is the moving direction of the slider S.
Such a grease nipple 3 has a ball 3a covering the supply port. The ball 3a functions as a check valve that permits lubricant flow for supply only in one direction from the lubricant supply nozzle toward the lubricant supply port. Accordingly, when the lubricant supply nozzle is pressed against the supply port for lubricant supply, a supply pressure is produced and retracts the ball 3a from its home position, so that the lubricant is introduced to the rolling-element directing passage via the lubricant supply port.
After the lubricant has been adequately supplied to the rolling-element directing passage, the lubricant supply nozzle is removed from the supply port, whereupon the supply port is covered again with the ball, so that foreign substances are prevented from entering from the supply port.
A structure as described above is described in Japanese Patent Laid-open No. 2000-120989.
A related-art side seal designed as described above has a grease nipple 3 protruding in the moving direction of the slider S, so that the stroke of the slider S is restricted by the length of the protrusion of the grease nipple 3. In particular, the linear motion guide units have been increasingly reduced in size in recent years. The more the size of the linear motion guide unit is reduced, the higher the ratio of the protrusion length of the grease nipple 3 to the stroke of the slider S. This produces the disadvantage that the stroke of the slider S is relatively restricted.
The related-art side seal needs the grease nipple 3 as described above. This gives rise to disadvantages of an increase in component count and an increase in cost.
In addition, since the grease nipple needs a ball for covering the supply port and a spring for pressing the ball against the supply port, the structure of the grease nipple itself is complicated, which is one factor responsible for the increased cost.
Precise fitting and close contact of the lubricant supply nozzle to the lubricant supply port of the grease nipple are required for the use of the lubricant supply nozzle to supply the lubricant to the lubricant supply port of the grease nipple without leakage. However, since the site where the grease nipple is mounted is located in an area that does not allow allocation of enough room for mounting the grease nipple, it is not easy to precisely press the leading end of the lubricant supply nozzle against the lubricant supply port of the grease nipple without misalignment, for the supply of lubricant without lubricant leakage.